1. Field of Invention
The present invention relates to a servo control apparatus and more particularly to a servo control apparatus which realizes accurate positioning by a positioner in the servo drive system.
2. Description of the Prior Art
As an example of such a servo control apparatus, a known apparatus positions a head for magnetically recording information on the recording surface of magnetic disk and reproduces such recorded information from the recording surface of the magnetic disk, for example, as disclosed in U.S. Pat. No. 4,488,187 "Servo Control Apparatus". This apparatus generates, as a positioning means, a first pulse group and a second pulse group in order to read first servo data and second servo data and stores the respective pulse groups by individually counting them. However, such means for obtaining servo control data is complicated, and the structure of the apparatus becomes large in size and accordingly the apparatus itself becomes expensive.
Meanwhile, another known apparatus has the structure which compares servo information with a reference level. In this case, however, it is impossible to always execute accurate positioning of head because the reference level of such comparison means changes in accordance with temperature, etc.